There is this pure java implementation: https://github.com/eclipse/milo of an UPC-UA Client/Server. Now I guess it shouldn't be too hard to implement this for an android application.
So my current progress is an empty android project, where I try to import the OPC Java-sdk. But since this isn't a JAR file, I can't import it properly...
Currently the artifact is only available from the Sonatype OSS snapshots repository because there are no releases yet.
fernandospr's answer is correct though, but you would need to either add the Sonatype OSS repository reference or clone the project and run
Now for the unfortunate part: Milo is written in Java 8, so it's unlikely you're going to get it working on Android.